Effects of low clay concentrations on nearly isotropic turbulence

We conducted laboratory experiments to quantify the effect of low concentrations of clay, C [0,2]%, on turbulence in water-clay flows under nearly isotropic conditions using a novel approach. Full optical access was possible using Laponite RD™, a synthetic clay capable of producing clear suspensions of clay particles. Turbulence was generated in a customized cubic mixing box using flow actuators placed symmetrically at each of the eight corners. High-frame-rate particle image velocimetry was used to quantify the spatiotemporal dynamics of turbulence around the center of the mixing box. The results showed that the presence of clay particles strongly modulated the structure of turbulence. Monotonic reduction of the turbulent kinetic energy (TKE) and mean dissipation rate (ϵ) and increase of the Taylor microscale λ was induced by increasing the clay concentration. In particular, the measurements indicated a relation between clay concentration and the p factor, the known Kolmogorov power-law correction -5/3+p(Reλ) of the inertial subrange, where Reλ is the Taylor microscale Reynolds number. The p factor decreased approximately linearly within 1% C2%. This parameter and the third-order structure function S3 supported the scale changes obtained from direct estimation with particle image velocimetry (PIV) data. These results demonstrated the significant impact of clay on the multiscale dynamics of turbulence even at low clay concentrations.